calcium and magnesium i am using a supplement for skimming i have a coral life skimmer...rated for 65 gallons my tank is a 55 gal... i have a 55 gallon tank my other means of nutrient export are a canister filter with a small amount of carbon, polishing pad and few pieces of live rock in it my alkalinity is sitting at 1.020
Please plan to change your skimmer. You can get much better than that! The fact that it is rated for a 65gal. doesn't mean anything most times. The quality and design is what makes a good skimmer! The investment is aways worthy!
You don't need canister for carbon. Place the carbon in the sump inside a mesh bag. Make sure your carbon is a good one. Many could leach phosphates to the water!
If you don't have sump please plan for one. Polishing pad doesn't export much nutrients. The biological filtration is done by the bacteria on/in the rocks. If you have many fishes per square inches you need more filtration (surface area) and you'll need to do partial water changes to be able to maintain the system running without nutrient problems. Do not overfeed.
Alkalinity is not the same as specific gravity ("salinity").
Specific gravity at 1.023 or 1.024 would be fine.
Alkalinity between 8 - 10 dKH is fine. The balance between alk and Ca is important.
Alkalinity is important, but please make sure you know that many times the combination of factors could be responsible for most problems with zoas, besides predation.
Your system looks very young and needs to mature in order to be able to keep the ionic and nutrient balances the inverts need.
When you add the new light it will go trough a series of changes and you need to go very slow so you don't shock the organisms! Also the water chemistry needs to be changed slowly.
Make sure you're not introducing phosphates into the system and that nitrates is always in check. Keep a good partial water change schedule. Search for useful additives and use them as directed or less than that, as needed!
Many things...
Try to reduce the number of fishes.
Study more about the water chemistry and maintenance in general.
Maintenance and stability are a must for closed systems!
Your system needs a little more time.
Good luck!
Grandis.